Magnet frame and coil assembly for thermoelectric safety devices and mounting therefor



July 24, 1956 G. l. HOLMES 2,756,371

MAGNET FRAME AND COIL ASSEMBLY FOR THERMOELECTRIC SAFETY DEVICES AND MOUNTING THEREFOR Filed Aug. 10, 1951 2 Sheets-Sheet l 4 34 Iii NH INVENTOR. l7 '/7 Gig ford Z ffolmcs July 24, 1956 G. 1. HOLMES 756,371

MAGNET FRAME AND COIL ASSEMBLY FOR THERMOELECTRIC SAFETY DEVICES AND MOUNTING THEREFOR Filed Aug. 10, 1951 2 Sheets-shat 2 fif 2 29 g6 IN V EN TOR.

.17 Z Gyfogd f 0 mes MAGNET FRAME AND COIL ASSEMBLY FOR THERR XGELECTRIC SAFETY DEVICES AND MOUNTIIJG THEREFOR Gifiord I. Holmes, Waukesha, Wis, assignor to hit:-

wauiree Gas Specialty Company, Milwaukee, Win, a corporation of Wisconsin Application August 10, 1951, Serial No. 241,233

8 Claims. (Cl. 317- 165) This invention relates, in general, to thermoelectric safety shut-off devices, and has particular relation to an improved magnet frame and coil assembly for such devices, and an improved mounting for the magnet frame and coil assembly.

In thermoelectric safety shut-off devices of the type with which the present invention is particularly adapted to be used, the thermoelectric generator is usually positioned where its one or more hot junctions will be heated by the flame of a pilot burner which is disposed in lighting proximity to a main burner. The current obtained from the heated thermoelectric generator is conducted by conductor leads to the coil of the magnet frame and coil assembly. Magnetic flux established in the magnet frame holds an armature in attracted position and, for example, a valve open or a switch closed as long as the pilot burner flame is burning. When the pilot burner flame is extinguished, the electromagnet, comprising the magnet frame and coil assembly, ceases to hold the armature in attracted position, and the valve closes, for example, by the force of a spring, or the switch opens to shut off the flow of fuel preferably to both the main burner and the pilot burner.

Since the amount of electromotive force that can be generated, for example, by the heat of the flame of a pilot burner on the one or more junctions of a thermoelectric generator is relatively minute, it is usually desirable to form the magnet frame of a special alloy which is noncorrosive and has a high degree of permeability With minimum retentivity. These special alloys comprise a high nickel content and are expensive.

Heretofore in the art it has been a practice to employ a magnet frame of generally U-shaped form with one or more coils wound around one or both of the extending legs of the magnet frame. it has also been a practice to mount the magnet frame, for example, on a terminal bushing by forming on the bushing a neck which extends through an opening in the base of the magnet frame and is spun over to secure the magnet frame to the bushing. A further practice has been to extend one end of the coil wire through the neck on the bushing, and thereby through the opening in the base of the magnet frame.

The provision of an opening in the base of the magnet frame has reduced the effective magnetic flux path along the base of the magnet frame. To provide suflicient effective magnetic flux path, it has been customary to increase the cross-sectional area of the base of the magnet frame to compensate for the cross-sectional area rendered ineffective as a magnetic flux path by the opening in the base of the magnet frame. This increases the amount of critical material that must be employed, and increases the size, Weight, and cost of the magnet frame and coil assembly. In other words, to provide sufiicient cross-section along the portion of the base of the magnet frame where the opening is disposed, excess material has been employed along the remaining portions of the base of the e magnet frame.

in operation, such prior devices have not been as effinited States Patent cient as may be desired, because saturation With magnetic flux of the reduced section of the base of the magnet frame where the opening is disposed may take place and therefore constitute a limiting factor while the remaining portions of the base of the magnet frame are unsaturated. Moreover, the increase in the cross-sectional area of the magnet frame has required larger diameter wire and more turns of same for the coil, which has further increased the size, weight, and cost of the device.

Winding of the coil or coils around one or both of the extending legs of the magnet frame has also made it necessary to make these legs relatively long. This increases the length of the magnetic flux path, and further adds to the size, weight, and cost of the device.

One of the main objects of the present invention is to provide an improved magnet frame and coil assembly wherein the cross sectional area of the magnet frame, the magnetic path, the diameter of the wire, and the number of turns of the same for the coil may all be reduced to a minimum. This is advantageous in that it reduces the amount of special material required and the size, weight, and cost of the magnet frame and coil assembly.

Another and more specific object of the invention is to eliminate the necessity for an opening in the base of the magnet frame and to enable shortening the legs of the magnet frame.

Another object of the invention is to provide a magnet frame having legs projecting laterally from the sides of the base of the magnet frame, whereby to provide expanded pole faces at the ends of these legs and guides and retention for the coil.

Another object of the invention is to provide a magnet frame which will function more efliciently, and, more particularly, a magnet frame having a base around which the coil is wound, which base may, in the operation of the device, be saturated, or substantially saturated, with magnetic flux throughout its entire cross sectional area and throughout its entire extent.

Further objects and advantages of the invention will appear from the following detailed description taken in conn ction with the accompanying drawings.

In the drawings:

Figure l is a longitudinal axial section through a complete hood assembly containing a magnet frame and coil assembly embodying the present invention, and showing more or less diagrammatically a thermoelectric generator in circuit with the coil wire and positioned where it will be heated by the flame of a pilot burner disposed in lighting proximity to a main burner;

Figure 2 is an elevational view of the inner end of the magnet rame and coil assembly as supported on the terminal bushing, and with the cup which encloses the armature and the magnet frame and coil assembly removed;

Figure 3 is a fragmentary detail section showing one form of connection between the valve stem and the armature;

Figure 4 is a front elevational view of the magnet frame;

Figure 5 is a bottom plan view of the magnet frame;

Figure 6 is an end view of the magnet frame looking from the right hand end as it is shown in Figure 5;

Figure 7 is a front elevational view of the supporting bracket for the magnet frame; and

Figure 8 is an end view of one of the inturned ends of the supporting bracket shown in Figure 7.

Referring now to the drawings, the burner shown at is a main burner. It may be the main burner for a oom or space heater, or it may be the burner for a water heater or for a floor furnace, an oven burner, one or more top burners for a gas range, or any other burner and of any suitable construction.

A fuel supply pipe or conduit 2 leads to the burner 1 for the delivery of gaseous or other fuel thereto, for example, through a mixing chamber 3 to which air is admitted through adjustable air inlets (not shown) as well understood in the art.

The flow of gas through the conduit 2 is in the direction indicated by the arrow 4, and is controlled by a valve member 5. The valve member 5 is shown in closed position seated upon an annular valve seat 6 at one end of a valve opening 7 formed, for example, in a partition within the valve body which is shown fragmentarily and diagrammatically at 8. Contiguous sections of the fuel supply pipe 2 are connected to the inlet 9 and outlet 10 of the valve body.

The pilot burner 11, which is located in juxtaposition to the main burner 1 to maintain a pilot flame for igniting the main burner and a flame for heating the thermoelectric generator as will presently appear, is supplied with gaseous fuel by a pilot supply pipe 12. The pilot fuel supply pipe 12 may be connected, for example, to the pipe 2 anterior of the valve member 5, or through the valve body 8, or to any other source of fuel supply. The positions of the pilot burner flames are shown in dotted lines for purposes of illustration.

The magnet frame, terminal bushing, terminal tip, and coil assembly selected for illustration comprise a U-shaped magnet frame 15. The magnet frame 15 is preferably formed of a special alloy which is non-corrosive and has a high degree of permeability, with minimum retentivity. Although the present invention is in nowise limited thereto, Permalloy (which is an alloy composed of approximately 80% nickel and iron), and Alleghany 4750 (which is an alloy composed of approximately 50% nickel and 50% iron) are suitable alloys for the magnet frame 15. The use of Armco iron (which has characteristics somewhat similar to Swedish electrolytic iron and is substantially pure iron) and other irons is contemplated within the scope of the present invention.

The magnet frame has an imperforate base 16 of minimum cross-section, and legs 17 of minimum length extending from opposite ends of the base. Although the present invention is not limited to particular dimensions for the magnet frame, the dimensions of one satisfactory device will now be given to show the small size and weight of such a device which the present invention makes possible. The dimension 18 of each leg 17 longitudinally of the magnet frame may be .118 of an inch. The length 19 of each leg 17 may be approximately .220 of an inch. The width 20 of each leg 17 laterally of the magnet frame may be approxi mately .5 of an inch. The base 16 may be of a length 21 between the legs 17 of approximately .264 of an inch; of a thickness 22 lengthwise of the legs 17 of approximately .118 of an inch; and of a width 23 laterally of the magnet frame of approximately .320 of an inch.

A coil 25 of wire of minimum diameter and a minimum number of turns is wound around the base 16 of the magnet frame. Further to illustrate one particularly satisfactory embodiment of the invention, the coil 25 for the magnet frame of approximately the above stated dimensions may comprise approximately 12 inches of approximately No. 22 copper wire.

A metallic or conducting terminal bushing 26 has an aperture 27 therethrough in register with an aperture 28' in the base 29 of a generally U-shaped supporting bracket 30. A tubular neck 31, integral with the bushing 30, extends through the aperture 28 in the base 29 and is spun over at 32 to secure the bracket firmly to the bushing 26. The legs 33 of the bracket 30, which are shown as diverging slightly from the base 29, straddle the magnet frame 15 and have inturned ends 34 which engage (detachably, if desired) in recesses or transversely elongated slots 35 in the opposite ends of the magnet frame. The inner ends of the slots 35 may be of arcuate contour, formed, for example, by cutting them with a one-half inch diameter cutter 36 as shown in dotted lines in Figure 5, but this may, of course, vary.

The magnet frame 15 is thus mounted without providing an aperture in the base 16 around which the coil is wound. This enables making the base 16 of minimum cross section; also so that it will be effective as a magnetic flux path throughout its entire cross-section; and so that in the operation of the device the base 16 may be saturated, or substantially saturated, with magnetic flux throughout its entire cross-sectional area and throughout its entire extent.

With the coil 25 wound on the base 16, the legs 17 of the magnet frame may be of minimum length. This provides a magnetic flux path of minimum length and, with the other distinguishing features, reduces the size, weight, and cost of the magnetic frame and coil assembly.

The outer end of the bushing 26 has a depression in which there is a terminal tip 36 of brass or other suitable conducting material. Packing or insulating sealing material 37 is interposed between and serves electrically to insulate the terminal tip 36 from the bushing 26. The material 37 is preferably one which is resistant to gaseous hydrocarbons so as to form a gas-tight joint between the bushing 26 and the terminal tip 36.

One end of the coil wire 25 extends through the tubular neck 31 and out through a registering aperture in the terminal tip 36, and is welded at 38 to a conically raised surface on the terminal tip 36. The coil wire 25 is preferably insulated at 39 by a suitable insulating wrapping. An annular insulating packing ring 40 is positioned about the outer margin of the outer surface of the terminal tip 36, and an integral annular flange on the terminal tip 36 is bent or spun over against the packing to provide gas-tight relation between the receptive parts of the device. The ring 40 is also preferably formed of insulating material which is resistant to gaseous hydrocarbons.

A magnet hood or cup is positioned over the magnet frame and coil assembly, and is spun at 46 into engagement with the terminal bushing 26. A stem 47 is mounted for reciprocatory movement through an opening formed by an eyelet 48 in the base of the cup 45. An armature 50 is mounted for relative movement on the inner end of the stem 47 to permit self-accommodation to the pole faces at the ends of the legs 17 of the magnet frame, for example, by extending the reduced inner end of the stem 47 through an opening in the armature 5t) and swaging the inner end of the stem at 51.

The valve disc is retained on the opposite end of the stem 47 by a retaining ring 52, and a coiled spring 53 is interposed between the valve disc and a valve spring seat 54 between which and the adjacent end of the hood 45 packing or sealing material is interposed at 54 to provide a gas-tight seal. The valve disc gasket 5 is clamped against the valve disc part 55 by a valve disc screw 56 screwed on the valve disc part 55.

The thermoelectric generator 60 is shown in the form of a thermocouple having elements of different thermoelectric characteristics joined at 61 to form the hot junction. The thermoelectric generator may be in the form of a thennopile, or of any other suitable form. The hot junction 61 is disposed in the pilot burner flame or where it will be heated by the flame of the pilot burner 11 as long as the pilot burner is ignited. One side of the thermoelectric generator is connected, for example, by a conductor 62 in circuit with the welded contact at 38, and thus to one side of the coil 25. The other side of the thermoelectric generator 60 is connected by a conductor 63 in circuit with the terminal bushing 26. The other side of the coil 25 is connected to the terminal bushing 26, for example, by a resistance weld at 64.

Where energization of the electromagnet comprising the magnet frame 15 and coil 25 is insuflicient to move the armature from its'retracted' position in which it is shown, to attracted position, and the valve .5 to open position, reset means (not shown) may be provided for resetting the device as is well understood in the art.

With the armature thus reset to attracted position, upon ignition of the pilot burner 11 the flame thereof, by heating the one or more hot junctions of the thermoelectric generator 60, energizes the electromagnet to hold the armature 50 in attracted position and the valve member 5 in open position.

If the pilot burner 11 is extinguished, or the circuit for the thermoelectric generator 60 is opened or disabled, the electromagnet ceases to hold the armature 50 in attracted position. The valve 5 is thereupon closed against the valve seat 6, for example, by the spring 53 to shut off the flow of fuel to the main burner 1, and preferably also the flow of fuel to the pilot burner.

The lateral or transverse projection of the legs 17 from the sides of the base 16 of the magnet frame provides expanded or enlarged pole faces at the ends of the legs 17 which eliminates or reduces magnetic flux leakage. The laterally projecting legs 17 also provide guides and endwise retention for the coil 25.

The cited example of a device embodying the present invention will exert substantially one and one-half pounds of force when the armature is engaged with the pole faces of the magnet frame.

The embodiment of the invention shown in the drawings is for illustrative purposes only, and it is to be expressly understood that said drawings and the accompanying specification are not to be construed as a definition of the limits or scope of the invention, reference being had to the appended claims for that purpose.

I claim:

1. In a device of the class described, in combination, a magnet frame of generally U-shaped form having an imperforate base of uniform cross-section and a pair of legs extending from the opposite ends of said base, said legs having a combined length no greater than the length of said base and projecting laterally from the sides of the base, said legs having a cross-sectional area larger throughout than said base and providing expanded fiat coplanar pole faces at the ends of said legs, an armature movably mounted to coact with the pole faces of said magnet frame, means biasing said armature away from said pole faces, means providing a source of electrical energy of limited magnitude, a coil of wire wound around the base of said magnet frame between said legs and connected in circuit with said source of electrical energy, said coil composed of the minimum number of turns and wire of the minimum diameter necessary to create a magnetic flux through said magnet frame sufiicient only to hold the armature at said pole faces in opposition to the bias exerted by said biasing means, and said base having a cross-sectional area large enough only to be substantially saturated by the magnetic flux induced by said coil.

2. In a device of the class described, in combination, a magnet frame of generally U-shaped form having an imperforate base of uniform cross-section and a pair of legs extending from the opposite ends of said base, said legs having recesses at opposite ends of said magnet frame and terminating in a pair of pole faces, an armature movably mounted to coact with the pole faces of said magnet frame, means biasing said armature away from said pole faces, means providing a source of electrical energy of limited magnitude, a coil of wire wound around the base of said magnet frame and connected in circuit to said source of electrical energy, said coil composed of the minimum number of turns and wire of the minimum diameter necessary to create a magnetic flux through said magnet frame sufficient only to hold the armature at said pole faces in opposition to the bias exerted by said biasing means, said base having a cross-sectional area large enough only to be substantially saturated by the magnet flux induced by said coil, and a bracket comprising a bracket base and a pair of extending bracket legs having converging ends engaged in said recesses to support said magnet frame between said bracket legs.

3. A device according to claim 2 wherein the base of said bracket has an aperture, a terminal bushing having an aperture therethrough in register with the aperture in the base of said bracket, and a neck on said terminal bushing extending through the aperture in the base of the bracket and securing said bracket to said terminal bushing.

4. A device according to claim 3 wherein the neck on the terminal bushing is of tubular form with one end of the coil wire extending through the tubular neck and to a contact at the outer side of said bushing.

5. In a device of the class described, in combination, a supporting bracket of generally U-shaped configuration having a base for attachment to a support and spaced extending legs, a magnet frame of generally U-shaped form having an imperforate base of uniform cross-section and a pair of legs having recesses at opposite ends of said magnet frame, the legs of said bracket having converging ends engaged in said recesses to support the magnet frame between the legs of said bracket, and a coil of wire wound around the base of said magnet frame between said legs.

6. A device according to claim 5 wherein the legs of said U-shaped magnet frame have a combined length no greater than the length of said base and project laterally from the sides of the base of the magnet frame and are expanded to provide expanded pole faces at the ends of said legs.

7. A magnet frame and coil assembly comprising a magnet frame of generally U-shaped form having an imperforate base of uniform cross-section and adapted to be substantially saturated with magnetic flux throughout its entire cross-sectional area and throughout its entire extent, a coil of wire wound only around the base of said magnet frame, said magnet frame having a pair of legs extending from the opposite ends of said base, said legs projecting laterally from the sides of the base and expanded throughout their entire extent to provide expanded flat coplanar pole faces at the ends of said legs and having attachment slots at opposite ends of said magnet frame for mounting said magnet frame and coil assembly.

8. A magnet frame of generally U-shaped form having an imperforate base of uniform cross-section and effective as a magnetic flux path throughout its entire cross-section, said magnet frame having a pair of legs extending from the opposite ends of said base, said legs having a combined length no greater than the length of and a cross-sectional area larger throughout than the cross-sectional area of said base and projecting laterally from the sides of the base to provide expanded fiat coplanar pole faces at the ends of said legs, said legs also having attachment slots at opposite ends of said magnet frame for mounting said magnet frame.

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